I had very vivid dreams when I started taking it (and could have written books), which subsided with time. But never nightmares.
That reminds me, I am on a PPI (prevacid). Been so for years (way longer than anyone should be on these things but have no choice supposedly because of horrendously bad acid reflux disease due to a floating hiatal hernia causing a weak lower esophogeal sphincter (LES)).
One of the known side effects of PPIs is very vivid dreams. I noticed this right away on the first PPI I was on (aciphex, which after about 2 years stopped working & then got put on prevacid). Those dreams were (are) amazing and usually fun. Also just as part of my normal brain for some reason I've always had pretty cool dreams, some I used to write down when I woke up b4 they faded. On a PPI I wish I had one of those brain scanner things from the movie Brainstorm though because they were so realistic yet bizarre/impossible (for example a few days ago I had a dream that my Mom - who passed away long ago - was still "alive" and her essence was living in this metal box thing where she could talk to us)..
Never had any nightmares like the ones on metoprolol b4 though (super vivid and realistic, dreams within dreams) and wonder if the PPI - and my normal way of dreaming in the first place - had something to do with it, pushed over the edge by metoprolol.
Anyways, trying to find the forum/posts now where I read about others complaining of nightmares I found this which perhaps touches on some of this:
https://somnustherapy.com/the-effect-of-metoprolol-on-sleep/
The comments I referred to about nightmares may have come from one of these sites:
https://www.drugs.com/comments/metoprolol/https://reviews.everydayhealth.com/drugs/metoprololhttps://www.webmd.com/drugs/drugreview-8814-metoprolol-succinate-oral
I haven't found the specific one about the woman talking about her husband but there are some comments mentioning nightmares. It was about 5 years ago that I read it so I would have to go back to that sort of timeframe in the sites above.
Also reading some of the comments above now it reminds me that I also experienced lack of sexual drive/performance (common with beta blockers I believe) plus even had some really weird blurred vision that people mention. On the plus side something beneficial that happened was that for around 4-5 months - even though only on the metoprolol for less than a month - I had no migraines at all - unlike my usual 5 or so a month that I've had ever since my open heart surgery (although right after the surgery I had more than one migraine a day, which slowly tailed off after like 3 months to become about 5 per month).
As I think I already said though the worst with metoprolol for me was the utter lack of energy, making it impossible for me to do almost anything but sleep/lie in bed, and the problems with thinking/concentrating/getting lost trying to drive to the Dr etc, which did not go away until I was told to cut the pills in half (but even on 1/2 dose I still had some probs).
I'll keep looking for the nightmare posts when/if I get more time.